The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Recently, increase of oil price leads more competition for improving fuel efficiency of a vehicle.
In this sense, research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages.
In order to achieve more shift stages for an automatic transmission, the number of parts is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency.
Therefore, in order to enhance fuel efficiency of an automatic transmission through more shift stages with reduced number of components, a planetary gear train for an automatic transmission enabling more shift-stages has been developed.
We have discovered that since an automatic transmission for eight or more shift-stages typically includes three to four planetary gear sets and five to six engagement elements (frictional elements), and the transmission may easily become lengthy, thereby deteriorating installability.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.